I use the Campaign Monitor API to feed subscribers in to C.M. from a subscribe form on my site. I pass in the email address, and a unique identifier hex key as a custom field.
I set C.M. to send a confirmation email to each new subscriber. I can successfully use the subscribers email address as a custom field in the confirm email, but not my custom hex key field. I think this is because the confirm email gets sent before the subscriber with the hex key data gets added to my list in C.M.
I need to be able to include my custom field in the confirmation email.